Abstract: A tamper-proof wall-mounted modular sign includes a low cost wall-engaging threaded member together with a mating threaded retainer having a concealed anti-rotation device, functioning in combination to securely mount the sign base plate and its protective overlay on the wall in a manner precluding theft or unauthorized alteration of the sign. The cylindrical retainer is significantly larger in diameter than the threaded member and receives the exposed end of the member in enveloping relation thereto such that there is created a desired illusion of solid support for the sign substantially greater than that actually presented by the threaded member. In preferred forms, a threaded spacer having a transverse cross-section identical to that of the retainer is supported on the threaded member between the wall and the base plate to give the sign an aesthetically pleasing appearance of floatation and for further enhancing the illusion of substantial support.